1. Field of the Invention
This invention relates to semiconductor packaging technology, and more particularly, to a layout method for a semiconductor package substrate with a plating bus, such as a TFBGA (Thin & Fine Ball Grid Array) substrate, which can help allow each singulated package unit from the TFBGA substrate to be substantially free of trace short-circuits due to misaligned cutting during singulation process.
2. Description of Related Art
BGA (Ball Grid Array) is an advanced type of semiconductor packaging technology which is characterized in the use of a substrate whose front surface is used for the mounting of a semiconductor chip thereon, and whose back surface is used for the mounting of a grid array of solder balls to allow the entire package body to be mechanically bonded and electrically coupled to an external printed circuit board (PCB). This structure allows the BGA package to be made very compact in size.
TFBGA (Thin & Fine Ball Grid Array) is a downsized type of BGA technology that provides semiconductor packages in very small sizes, which are customarily fabricated in batch from a single large-size chip carrier, such as a substrate. The large-size TFBGA substrate is predefined with a matrix of package sites, and an individual TFBGA package unit can be obtained by cutting apart each package site from the TFBGA substrate through singulation process.
In layout design, a TFBGA substrate is typically predefined with a great number of bond pads, electrically-conductive traces, and solder-ball pads, which are separately located at different locations all over the package sites. During the TFBGA fabrication, it is required to plate an electrically-conductive material, such as the alloy of nickel and gold (Mi--Au), onto these traces and pads to make them highly conductive to electricity. To facilitate the plating process, these traces and pads are all connected in layout design to, a provisional plating bus, which is used to conduct electricity to al the traces and pads during plating process, and which can be cut away in the final singulation process.
A conventional layout method for TFBGA substrate with plating bus is depicted in the following with reference to FIGS. 1A-1C.
FIG. 1A shows a schematic plan view of the front surface of a TFBGA substrate 100 utilizing a conventional layout method (note that FIG. 1A is simplified to show only a small number of electrically-conductive trades and via lands for demonstrative purpose; the actual layout may be much more complex).
As shown, this TFBGA substrate 100 is predefined into a plurality of package sites (only two are shown in FIG. 1A, respectively designated by the reference numerals 110a, 110b) which are delimited by a plurality of crosswise and lengthwise singulation lines SL.sub.X, SL.sub.Y. In the final singulation process, the respective package sites 110a, 110b can be cut apart into individual package units along these predefined singulation lines SL.sub.X, SL.sub.Y.
These package sites 110a, 110b are predefined with the sane circuit layout, wherein the package site 110a is predefined with at least one die-mounting area 111a which is associated with a plurality of crosswise-extending electrically-conductive traces 112a and two rows of via lands 113a located on both sides of the die-mounting area 111a and alongside the nearby lengthwise singulation lines SL.sub.Y, and similarly, the neighboring package site 110b is predefined with at least one die-mounting area 111b which is associated with a plurality of crosswise-extending electrically-conductive traces 112b and two rows of via lands 113b located on both sides of the die-mounting area 111b and alongside the nearby lengthwise singulation lines SL.sub.Y.
The via lands 113a, 113b define the locations where electrically-conductive vias (not shown) are formed to interconnect the electrically-conductive traces 112a, 112b on the front surface of the TFBGA substrate 100 with the solder-ball pads (not shown) on the back surface of the same. Since the fabrication of these vias (not shown) and solder-ball pads (not shown) is not within the spirit and scope of the invention, description thereof will not be further detailed.
During the TFBGA fabrication, it is required to perform plating on the bonding finger area 111a, 111b electrically-conductive traces 112a, 112b on the front surface and the solder-ball pads (not shown) on the back surface. To facilitate the plating process, the via lands 113a, 113b are all connected to a common plating bus 120, so that the electricity used during the plating process can be applied to the plating bus 120 and then concurrently distributed by the plating bus 120 by way of the via lands 113a, 113b and the electrically-conductive traces 112a, 112b to the bonding finger area 111a, 111b on the front surface and the solder-ball pads (not shown) on the back surface of the TFBGA substrate 100.
In layout design, the plating bus 120 is formed in a grid shape and laid directly over the crosswise and lengthwise singulation lines SL.sub.X, SL.sub.Y, so that in the final singulation process, the plating bus 120 can be entirely cut away.
One drawback to the forgoing layout method, however, is that, since the TFBGA substrate 100 is typically very small in size, where the plating bus 120 is typically from 0.05 mm to 0.1 mm (millimeter) in width and the cutting blade (not shown) used in the singulation process is typically 0.3 mm in width, the alignment of the cutting blade (not shown) to the singulation lines SL.sub.X, SL.sub.Y should be highly precisely controlled; otherwise, in the case that the misalignment exceeds 0.115 m, it would cause the problem of trace short-circuits.
As shown in FIG. 1B, when the cutting blade's position (designated by CB) is misaligned to the singulation line SL.sub.Y, then it would be likely to leave an edge part of the plating bus 120 beyond the cutting range.
As shown in FIG. 1C, in the case of an overly misaligned cutting during singulation process, a small edge part of the original plating bus (designated here by the reference numeral 121) might be left over the edge of the singulated package site 110a, which would cause the electrically-conductive traces 112a on the package site 110a to be short-circuited to each other. When this is the case, the singulated TFBGA package unit would be regarded as defective.
FIG. 2 shows a solution to the foregoing problem of trace short-circuits due to misaligned cutting during singulation process.
As shown, this improved layout method is utilized on a TFBGA substrate 200 predefined into a plurality of package sites (only two are shown in FIG. 2, respectively designated by the reference numerals 210a, 210b which are delimited by a plurality of crosswise and lengthwise singulation lines SL.sub.X, SL.sub.Y.
The package site 210a is predefined with at least one die-mounting area 211a which is associated with a plurality of crosswise-extending electrically-conductive traces 212a and two rows of via lands 213a located on both sides of the die-mounting area 211a and alongside the nearby lengthwise singulation lines SL.sub.Y. In largely the same manner, the neighboring package site 210b is also predefined with at least one die-mounting area 211b which is associated with a plurality of electrically-conductive traces 212b and two rows of via lands 213b located on both sides of the die-mounting area 211b and alongside the nearby lengthwise singulation lines SL.sub.Y. However, in order to facilitate this improved layout method, it is to be noted that the right row of via lands 213a within the first package site 210a are unaligned in line to the left row of via lands 213b within the second package sites 210b.
This improved layout method is characterized in that all of the via lands 213a, 213b that are laid on both sides of each lengthwise singulation line ST.sub.Y are all connected to a zigzag plating bus 220 extending in a zigzag manner along the lengthwise singulation line SL.sub.Y.
It can be easily seen from the illustration of FIG. 2 that even though there is misaligned cutting to the lengthwise singulation line SL.sub.Y, the unremoved part of the plating bus 120 would not cause the electrically-conductive traces 212a within the first package site 210a and the electrically-conductive traces 212b within the second package sites 210b to be short-circuited to each other. Therefore, the layout method shown in FIG. 2 can help eliminate the problem of trace short-circuits due to misaligned cutting during singulation process.
One drawback to the foregoing layout method shown in FIG. 2, however, is that it requires the electrically-conductive traces 212a within the first package site 210a to be unaligned in line to the electrically-conductive traces 211b within the second package sites 210b so as to facilitate the zigzag design for the plating bus 220. This unaligned layout pattern, however, would make the overall layout work highly complex and thus difficult to carry out.